1. Technical Field
The present invention relates to a silicone composition for use in the vicinity of electrical contacts in an open system or in sealed or semi-sealed electrical devices including electrical equipment and electronic devices which contain electrical contacts, and, for extended periods of time, will not cause conduction faults at electrical contacts caused by silicone vapor such as organosiloxane oligomer or cyclic siloxanes. The invention also relates to a method for preventing the conduction faults at electrical contacts which are caused by silicone vapor.
2. Prior Art
Various silicone products are used in electrical devices, electrical equipment, and electronic devices. For example, silicone oil is used as an electrical insulating oil in transformers and condensers; silicone greases and silicone compounds are used as lubricants, electrical insulation, and waterproofing agents; silicone resins and organosilanes are used as coatings; room temperature-curable silicone rubber compositions and low temperature-curing silicone rubber compositions are used as adhesives, sealants, casting agents, and coatings; silicone gel compositions are used as shock absorbers and casting agents; and thermosetting silicone rubber compositions are cured to give packings, O-rings, and electric wire coatings.
However, when such silicone products are used in the vicinity of electrical contacts in an open system (e.g., electrical switch contacts and electrical sliding contacts), or when they are used in sealed or semi-sealed electrical devices, electrical equipment, or electronic devices which contain electrical contacts, a decline in the conductivity of the electrical contacts is observed, and, in extreme cases, conduction may completely disappear. The electrical contact functionality is thus lost. The cause of this is that silicone products are typically based on organopolysiloxanes which are polymerized by equilibration polymerization and which thus contain residues of the starting material, as well as, volatile organosiloxane oligomer by-products. Moreover, another cause is that some silicone products are in fact based on volatile organosiloxane oligomer or organosilane, possibly in combination with organopolysiloxane. It is thought that the faulty conduction at the electrical contact is caused by the volatilization, at room or elevated temperature, of this organosilane or organosiloxane oligomer with a degree of polymerization (DP) of approximately 2 to 25. When this reaches the electrical contact, it undergoes a chemical change under the impact of the discharge energy generated upon operation of the contact and forms an insulating material such as silicon dioxide and silicon carbide, refer, for example, to Denki Tsushin Gakkai Gijutsu Kenkyu Hokoku, (Technical Research Reports of the Institute of Electrical Communication Engineers of Japan), 76 (226), pages 29-38, (1977).
The following means for solving this problem have been disclosed: equilibration-polymerized organopolysiloxane is heated in vacuo in order to thoroughly remove the contained organosiloxane oligomer; or the voltage and current loading conditions across the electrical contact are maintained within the limited range at which conduction faults do not occur, refer to Japanese Patent Application Laid Open [Kokai] Number 61-209266 [209,266/86], equivalent to U.S. Pat. No. 4,695,617, issued Sep. 22, 1987, to Inoue et al. Other proposals include compositions in which an amine or fluorinated organic compound is added to the silicone composition, refer to Japanese Patent Application Laid Open Number 63-270762 [270,762/88], published Nov. 8, 1988 and to Japanese Patent Application Laid Open Number 01-104656 [104,656/89], published Apr. 21, 1989, but also methods in which the presence of amine vapor or fluorinated organic compound vapor is induced in the silicone vapor, refer to Japanese Patent Application Laid Open Number 01-24325 [24,325/89], published Jan. 26, 1989 and Japanese Patent Application Laid Open Number 01-109615 [109,615/89], published Apr. 26, 1989.